The British security contractor accused of murdering two western colleagues in Baghdad and critically wounding an Iraqi appeared in court today and "made a full confession" about his role in the alleged rampage, according to a senior Iraqi official.

Daniel Fitzsimons, a former Paratrooper, appeared before an investigative judge who told him he faces the death penalty if convicted. Interior ministry spokesman Major General Abdul-Kareem Kalaph said last night that Fitzsimons had confessed during the brief hearing to shooting dead his colleagues.

"The British guard admitted his crime of killing the two men," said Kalaph. "He remains under investigation in the Green Zone on charges of premeditated murder. He faces the death penalty or life imprisonment, depending on the evidence."

Consular staff from the British embassy in Baghdad were last night trying to get access to Fitzsimons, who is being kept in an Iraqi prison inside the fortified Green Zone, not far from where he allegedly shot dead former British soldier Paul McGuigan, and former Royal Australian Airforce operative Darren Hoare during a drunken disagreement in a security company bar early on Sunday.

An embassy spokesman confirmed that Fitzsimons had attended court, but was still trying to establish whether he had made any admissions.

News of the speedy court appearance came as details of 29-year-old Fitzsimons and those of his alleged victims began to emerge.

Friends and former colleagues of Fitzsimons – who had spent eight years in the Parachute regiment – described him variously as a born military man as well as a "loose cannon".

One friend, Alex, who saw him when he was at home, told the Guardian: "He lived for it. It's the same old story. If you are part of the military, that's what you do. Being back home frustrated him."

Social networking sites he visited appear to paint a picture of an extrovert character with plenty of friends who enjoyed drinking and the camaraderie of army life.

His two victims worked for the same company as Fitzsimons – ArmorGroup, which has operated from Baghdad since shortly after Saddam Hussein was ousted in 2003. It is one of 54 private security companies now operating in Iraq, all of whom now fall under Iraqi law.

Amnesty International UK media director Mike Blakemore said: "As with all capital cases, Amnesty would strenuously oppose the application of the death penalty if applied to Mr Fitzsimons in this case. Iraq has a dreadful record of unfair capital trials. The important thing now is that, if Danny Fitzsimons is put on trial, he is allowed a fair trial process without resort to the cruelty of a death sentence."